Hepatitis C virus (HCV) is the leading cause of chronic liver disease worldwide and has become a focus of considerable medical research. HCV is a member of the Flaviviridae family of viruses in the hepacivirus genus, and is closely related to the flavivirus genus, which includes a number of viruses implicated in human disease, such as dengue virus and yellow fever virus, and to the animal pestivirus family, which includes bovine viral diarrhea virus (BVDV). The genome of HCV comprises both 5′ and 3′ untranslated regions that adopt RNA secondary structures, and a central open reading frame that encodes a single polyprotein. The polyprotein encodes ten gene products, which are generated from the precursor polyprotein by an orchestrated series of co- and posttranslational endoproteolytic cleavages mediated by both host and viral proteases. The viral structural proteins include the core nucleocapsid protein, and two envelope glycoproteins E1 and E2. The non-structural (NS) proteins encode some essential viral enzymatic functions (helicase, polymerase, protease), as well as proteins of unknown function. Replication of the viral genome is mediated by an RNA-dependent RNA polymerase, encoded by non-structural protein 5b (NS5B). In addition to the polymerase, the viral helicase and protease functions, both encoded in the bifunctional NS3 protein, have been shown to be essential for replication of HCV RNA. In addition to the NS3 serine protease, HCV also encodes a metalloproteinase in the NS2 region.
Following the initial acute infection, a majority of infected individuals develop chronic hepatitis because HCV replicates preferentially in hepatocytes but is not directly cytopathic. In particular, the lack of a vigorous T-lymphocyte response and the high propensity of the virus to mutate appear to promote a high rate of chronic infection. Chronic hepatitis can progress to liver fibrosis leading to cirrhosis, end-stage liver disease, and HCC (hepatocellular carcinoma), making it the leading cause of liver transplantations.
There are 6 major HCV genotypes and more than 50 subtypes, which are differently distributed geographically. HCV type 1 is the predominant genotype in Europe and the US. The extensive genetic heterogeneity of HCV has important diagnostic and clinical implications, perhaps explaining difficulties in vaccine development and the lack of response to current therapy.
Transmission of HCV can occur through contact with contaminated blood or blood products, for example following blood transfusion or intravenous drug use. The introduction of diagnostic tests used in blood screening has led to a downward trend in post-transfusion HCV incidence. However, given the slow progression to the end-stage liver disease, the existing infections will continue to present a serious medical and economic burden for decades.
Current HCV therapies are based on (pegylated) interferon-alpha (IFN-α) in combination with ribavirin. This combination therapy yields a sustained virologic response in more than 40% of patients infected by genotype 1 viruses and about 80% of those infected by genotypes 2 and 3. Beside the limited efficacy on HCV type 1, this combination therapy has significant side effects and is poorly tolerated in many patients. Major side effects include influenza-like symptoms, hematologic abnormalities, and neuropsychiatric symptoms. Hence there is a need for more effective, convenient and better-tolerated treatments.
A number of similar HCV protease inhibitors have been disclosed in the academic and patent literature. The sustained administration of HCV protease inhibitors usually leads to the selection of resistant HCV mutants, so called drug escape mutants. These have characteristic mutations in the HCV protease genome, notably D168V, D168Y and/or A165S. Accordingly, there is a need for additional drugs with different resistance patterns to provide failing patients with treatment options. Such drugs may find use in combination therapy, which is expected to become the norm in the future, even for first line treatment.
Experience with HIV drugs, in particular with HIV protease inhibitors, has taught that sub-optimal pharmacokinetics and complex dosing regimes quickly result in inadvertent compliance failures. This in turn means that the 24 hour trough concentration (minimum plasma concentration) for the respective drugs in an HIV regime frequently falls below the IC90 or ED90 threshold for large parts of the day. It is considered that a 24 hour trough level of at least the IC50, and more realistically, the IC90 or ED90, is essential to slow down the development of drug escape mutants.
Achieving the necessary pharmacokinetics and drug metabolism to allow such trough levels provides a stringent challenge to drug design. Known HCV protease inhibitors, with multiple peptide bonds, pose additional pharmacokinetic hurdles to effective dosage regimes.
There is a need for HCV inhibitors that may overcome the disadvantages of current HCV therapy such as side effects, limited efficacy, the emerging of resistance, and compliance failures.
The present invention concerns inhibitors of HCV replication that exhibit at least one improved property in view of the compounds of the prior art compounds. In particular, the inhibitors of the present invention are superior in one or more of the following pharmacological related properties, i.e. potency, decreased cytotoxicity, improved pharmacokinetics, improved resistance profile, acceptable dosage and pill burden. The HCV inhibitors of the present invention are particularly attractive due to their good activity against mutant HCV strains.